1. Field of the Invention
This invention relates to an adaptive control system which controls a physical plant such as a servo motor, a heat pump and the like with unknown dynamics and disturbances.
2. Description of the Prior Art
A conventional adaptive control system, the Time Delay Controller (TDC), has been proposed by K. YOUCEF-TOUMI and O. ITO, the inventor of this invention, in a paper, "A Time Delay Controller for Systems with Unknown Dynamics" in pages 904 through 911 of the Proceedings of 1988 American Control Conference.
The TDC deals with a physical plant expressed in a state space dynamic equation where an input distribution is known and the number of effective inputs is the same as the number of independent outputs. For this class of physical plants, an object of the TDC is to eliminate an error, which is defined as a difference between a desired output of a reference model and an actual output of a physical plant. In order to achieve the object, an unknown dynamics value is estimated using a time delay based on observation of inputs and state outputs. The TDC cancels the estimated unknown dynamics value, cancels an undesired known dynamics value, inserts a desired dynamics value of a reference model, and adjusts dynamics of the error. The above mentioned paper shows the TDC's excellent robustness properties to unknown dynamics and disturbances.
However, the TDC has the following three disadvantages from a practical point of view.
(1) A time delay is difficult to implement.
(2) The controller does not work successfully when either a state output value, a known dynamics value or an input distribution matrix value changes quickly.
(3) A reference model is not useful when an output of a physical plant should continuously follow a certain desired trajectory defined as a function of time.